Known as congestion pricing, the concept is favored by the US Department of Transportation, which is planning to help fund some of these efforts this summer. Nine cities – including such car-oriented cities as San Diego, Miami, and Dallas – are proposing a charge to use roads during rush hour. New York's is the most wide-sweeping – tacking on an $8 fee for cars and $21 for trucks to enter much of Manhattan.

Opponents call the proposal a regressive tax that hurts working people. And they worry about small businesses that count on commuters losing business.

Proponents of the system say it is a way to get more riders on mass-transit systems or at least in van or car pools. The model is London, which claims that such fees are now allowing traffic to flow more smoothly.

"The concept is certainly starting to spread," says Allison Hannon, a researcher at the Climate Group in New York, a nonprofit that tries to connect business and government to solve climate issues. "What happened is that London's Mayor Ken Livingstone and Oslo's mayor went out on a ledge and tried it, and it actually worked."

As almost anyone who drives in an urban area can attest, traffic jams don't seem to go away. In May 2005, the Texas Transportation Institute (TTI) at Texas A&M University found that congestion continued to grow in 85 regions it studied. Overall, traffic delays amounted to 3.7 billion hours in 2003, up from 700 million hours in 1982, the study found.

From an environmental standpoint, gridlocked traffic is also costly. Stalled cars have higher emissions than moving traffic, says Timothy Lomax of the TTI, who has been involved in urban-congestion studies for the past 20 years. "You can improve the emissions if you reduce the stop-and-go and move into a range of flow-and-go – say 30 to 40 miles per hour," says Mr. Lomax.

San Diego, in fact, has been charging commuters a congestion toll since 1997 to use special lanes of the I-15, the main inland north-south expressway. The toll itself changes, depending on the traffic, from 50 cents to as much as $8 if there is an emergency or a car breakdown. The users save an average of 10 to 15 minutes, but surveys show they think they save 30 minutes.

"The toll is dynamic. It has the ability to change every six minutes depending on the conditions," says Garry Bonelli, a spokesman for the San Diego Association of Governments (SANDAG), which develops long-term transportation plans for the region.

Now, SANDAG, at a cost of $1.7 billion, is expanding the toll road from two to four lanes. And it will be 24 miles long, up from eight.

Two years ago, San Francisco discussed adding a fee to enter the city, but it quickly ran into political opposition. City agencies are still discussing the issue, says Howard Strassner of the San Francisco Sierra Club in an e-mail. But the city, he says, may have something better than congestion pricing: a 20 percent tax on top of very high parking fees.

New York's proposal may run into stiff political winds as well. The state legislature must approve any new taxes or fees, and Sheldon Silver, speaker of the House, has been ambivalent about the concept. However, he has said he might call a special session of the Assembly this summer.

"My sense is the speaker will tend to his members," says Kathryn Wylde, president of the Partnership for New York City, which is largely made up of large businesses. "And if his members' concerns are fairly addressed, he will support it."

Some of those concerns were on display last week at a rally of an ad hoc group called the Committee to Keep NYC Congestion Tax Free. State Sen. Carl Kruger of Brooklyn complained the tax was unfair, "basically putting a tax on those who can't afford it." He called for more spending to alleviate traffic in the outer boroughs.

Queens Village resident Gabriella Krill thought the proposed tax would be unfair on seniors who already pay heavy taxes to live in the city. "Subways are hard – to go up and down stairs. Buses are hard to get out of," she said.

However, Ms. Wylde says the issue is too important to be sidetracked. Her office has put together briefing papers that show billions of dollars of lost business and thousands of lost jobs if nothing is done.

"If we don't do this now, it will never happen," she says. "And then New York will lose its leadership position."